popular fad diets 2013

thank you, it's a pleasure to be here. i'm an archaeological scientist and i study the healthand dietary histories of ancient peoples using bone biochemistry and ancient dna. i'm here because i wantto talk to you about the paleo diet. it's one of america's fastest growingdiet fads. the main idea behind it is that the keyto longevity and optimal health is to abandonour modern agricultural diets, which make us ill,

and move far back in timeto our palaeolithic ancestors, more than 10,000 years ago,and eat like them. now, i'm really interested in this idea because it purports to putarchaeology in action, to take information we know about the past and use it in the presentto help us today. now, this idea was really startedin the 1970s with this book, "the stone age diet." it's diversified since theninto several variants,

including the paleo diet,the primal blueprint, the new evolution diet, and neanderthin, and most of the language of these dietsmakes references to anthropology, nutrition science,and evolutionary medicine. the diet does seemprimarily targeted at men, so if you look at advertisementsand descriptions, they have virile, cavemen-like images, things like "live primal,"lots of red meat. and basically, the idea behind itcan be broken down into four parts.

one is that our agricultural diets todaymake us chronically ill, that they are out of syncwith our biology. and two, that we needto abandon these agricultural diets that startedduring the agricultural period, and move back in time to the palaeolithic and eat more like our ancestorsover 10,000 years ago. third, that we knowwhat these diets were like, and what they were like was they had a lotof meat, they were mainly meat based. that was supplemented with vegetablesand fruits and some nuts and oils,

but it definitely did not containgrains or legumes or dairy. and fourth, that if weemulate this ancient diet, it will improve our healthand make us live longer. so what i want to talk to you about todayis that this version of the paleo diet that's promoted in popular books,on tv, on self-help websites and in the overwhelming majority of presshas no basis in archaeological reality. so, thank you! (laughter) no, i'm not going to end there;i will explain.

so what i want to doas an archaeologist is go through this, do a bit of myth-busting of some of thesefoundational archaeological concepts upon which it's based, and then i want to talk to youabout what we really do know from the archaeological record and from scientific studiesabout what palaeolithic people did eat. so, myth one is that humansare evolved to eat meat and that palaeolithic peoplesconsumed large quantities of meat.

humans have no knownanatomical, physiological, or genetic adaptationsto meat consumption. quite the opposite, we havemany adaptations to plant consumption. take, for example, vitamin c. carnivores can make their own vitamin c,because vitamin c is found in plants. if you don't eat plants,you need to make it yourself. we can't make it, we haveto consume it from plants. we have a longer digestive tractthan carnivores. that's because our foodneeds to stay in our bodies longer,

so we have more timeto digest plant matter. we need more surface area,we need more microbes. we have generalist dentition, so we have big molars that are thereto shred fibrous plant tissue. we do not have carnassials, which are the specialised teeththat carnivores have to shred meat, and we do actually havesome genetic mutations in some populations that are adaptive to animal consumption,but it's to milk, not meat, and these arose in certain populationsduring agricultural periods

primarily in europe and africa. i call this "the meat myth." the idea behind itis that we should eat all this red meat, but that's just really not true. the meats on this plate of meat here are from fattened cattle,these are domestic animals. anything a palaeolithicperson would have eaten would have probably been very lean,probably small, and they wouldn't reallyhave eaten that much meat.

of course there's alsobone marrow and organs, these would have been very important. we see evidence of harvestingof bone marrow in faunal assembles where you see characteristiccutting open of the bones, like you see here, for marrow extraction. now sure, people did eat meat, and especially in the arctic and areas with long periodswhere plants were not available, they would have eaten a lot of meat.

but people that livedin more temperate or tropical regions would have had a very largeplant portion of their diet. so where does this meat myth come from? there's really two places, and one is the inherent biasin the archaeological record. bone is 80% mineral by weight,it's going to preserve better and longer over thousands of yearsthan delicate plant remains. but the other issue comesfrom some early bone biochemistry studies that were performedon neanderthals and early people.

this bone biochemistry study is based on something callednitrogen stable isotope analysis. it's complicated, but i'm goingto try and break it down. the basic idea is that you arewhat you eat, and so we - there's nitrogen-15 and nitrogen-14,heavy and light versions of nitrogen - and we consume this nitrogen in our food. but there's one important difference, and that is, with each stepthat you go up the trophic hierarchy, the amount of the heavierisotope increases.

so if you measurethe amount of heavy isotope in the bone, you can infer where that individualwas on a food chain. this is an exampleof a generalized isotopic model. i've plotted where plants generally fall,and above them are the herbivores, and then above them, the carnivores. but one of the problems is that not allecosystems conform to this model. there's a lot of regional variability,so if you don't understand the region, you can come to erroneous conclusions.i'll give you some examples: we can take east africa;if we measure animals and ancient humans,

in east africa, we seesome very strange patterns. first of all, how can a humanbe higher than a lion? lions only eat other animals. and then,how is this herbivore above a lion? well, it turns outthat the food that you eat is not is not the only contributorto these isotopic values. and that aridity can also have an impact. so what we're likely seeing hereis differences in water access. so let's move out of the savannahand move into the tropical areas. let's look at the ancient maya;again we see something anomalous.

we see the ancient mayalining up with jaguars. now, we know the ancient mayahad a diet heavily reliant on corn. so what's happening here? we don't exactly know,but we think this may have to do with the way they performed agricultureand how they fertilised their crops. now let's go to the pleistocene. we see somereally interesting patterns here too. we see reindeer plotting very low,in the range of plants. we see wolves plotting normallywhere you would see herbivores,

and we see mammothsspanning all three levels, at once plants, herbivores and carnivores. so what we think is happening here is that in very cold climates,animals eat unusual things. and in this casewhat we think is happening is these mammothsare eating lichens and bark and that's giving themvery strange values. so if we now go to humans, ancient humans,palaeolithic humans, and neanderthals, we see that they plot in the sameisotopic space as wolves and hyenas.

now that's true, but as i've shown,if you don't have good control over the regional isotopic ecology,you can come to an erroneous conclusion, and i think it's premature to say this is very strong evidenceof meat consumption, given how very little we really knowabout the palaeolithic ecosystems. so, myth two is that palaeolithic peoplesdid not eat whole grains or legumes. now, we have stone tool evidencefrom at least 30,000 years ago - that's 20,000 yearsbefore the invention of agriculture - of people using stone tools

that look like mortars and pestlesto grind up seeds and grain. more recentlywe've been developing techniques where we can actually measurethis thing called "dental calculus." it's very interesting:it's fossilized dental plaque. we can go in the individual mouthsof people, pull out that plaque and recover microfossilsof plants and other remains. my team is working on developingmethods to extract dna and proteins, and other research groupsare focussing on these microfossils like starch grains, pollen and phytoliths.

now, we're still in early days here, but even with the limitedresearch we have, we can say that there is an abundanceof plant remains inside the dental calculusof paleolithic peoples. and these things includegrains, including barley. we're finding barley insideneanderthal teeth, or inside the plaque. we also have legumes and tubers. so, myth three is that paleo diet foods,in the fad diet, are what our palaeolithic ancestors ate.

that's just not true. every single food that's picturedin these advertisements are all domesticated foods,products of farming, of agriculture. they're from the neolithic transition. let's give an example - bananas. bananas are the ultimate farmer's food. they can't reproduce in the wild anymore. we've bred out their abilityto make seeds. so every banana you've ever eaten

is a genetic clone of every other banana,grown from cuttings. they're definitely a farmer's food. if you were to eat a wild banana,it is so full of seeds that i bet many people in this roomwouldn't even recognize it as edible. let's take salads, that seemslike a really great paleo diet food. except that we've radically changedthe ingredients to suit our needs. so, wild lettuces containa great deal of latex, which is indigestibleand irritates our gastrointestinal system. it's bitter, the leaves are tough.

we've domesticated themto be softer, to produce bigger leaves, to remove the latex and the bitterness, remove the spines that grow on the leaves and stems of wild varieties,make them tastier for us. the tomato that's shown here lacks the tomatine and solanine toxinsthat are present in its wild relatives, which are all membersof the poisonous nightshade family. if we look at oil, it's true that oliveoil is the only natural vegetable oil that can be harvestedwithout synthetic chemicals.

except, it still requires at leastrudimentary presses to remove it, something that no palaeolithic personwould have ever built. this is a farmer's food. this is a model diet i found on a website. it looks like a deliciousand nutritious breakfast, but a palaeolithic personwouldn't have had access to it. first of all, the blueberriesare from new england, the avocados, from mexico,and the eggs, from china. this would havenever appeared on any palaeolithic plate.

and last, we have this problem of size. domestic blueberriesare twice the size of wild blueberries. we've already talkedabout bananas; you look at avocados. a wild avocado has maybea couple millimetres of fruit on it, and the same goes for wild olives. and of course chickens, chickensare prolific producers. they lay eggs almost every single day. they're predictable, large and abundant. if you're trying to collectwild eggs, they don't lay year round,

and they're not as easy to find,they're typically small. but maybe you're not convinced, so i'm going to givejust a couple more examples. this, you may all recognise as broccoli. broccoli did not even existin the palaeolithic period. what you see on the leftis wild broccoli - looks quite different. now, wild broccoli is also:wild cabbage, wild cauliflower, wild kale, wild kohlrabi and wild brussels sprouts,they're all the same species. the only difference is they'redifferent cultivars.

we've selectively bred the same species to produce the kind of foodthat we like best. these are human inventions. broccoli, i think, is an interestingexample because it's this weird thing. what even is broccoli? it's such a strange looking vegetable. in case you don't know, it's flowers,the flower of the plant. we've changed this wild plant into something that producesso many dense flowers.

it produces this odd,stalk-like thing, but it is flowers. if you don't believe me,buy some broccoli at your grocery store, put it in a vase, like i didon the right, and it will bloom. it makes a lovely, lovely bouquet. so let's talk about carrots next. you all recognise the carrotson the right, but wild carrot is what's on the left. it contains falcarindiol and otherthings that are natural pesticides. they're bitter in flavourand they taste really bad,

and we've bred them outand we've also expanded them made them much bigger, much sweeter,and much more full of vitamins, because that's what we want. many of you may not know this, but almonds and apricots are extremely closely relatedspecies of prune. the main difference is thatwe've bred out the cyanide in almonds, so that we can eat the seed, and we have selected for bigger,thicker fruits in apricots,

because that's what we wantto eat from that particular species. they're very closely related and,like carrots and broccoli, they are essentially human inventions. so let's talk about some real paleo diets. first of all, i need to clarifythat there is no one paleo diet. there are many, many paleo diets. people, when they spread outacross the world, colonised the continents, they ate local foods, and of coursethey were extremely variable.

so when we speak about palaeolithic diets, it's very importantto speak of them in the plural. let's take a closer lookat one in particular; we're going to go 7,000 yearsback in time to oaxaca, mexico, and right now you're looking at the viewoutside of the guilã¡ naquitz rock shelter, one of the earliest sites in mexico. this is a photographthat i took in december, and people would havebeen living here at this time, and what you are essentiallyseeing right now is dinner.

and this is a far cry from anythingthat you would find on the paleo diet and anything you would findin your modern supermarket. but, there was plenty of food herefor people to eat on a seasonal basis. so, september was high timeat guilã¡ naquitz. this is when a lot of peoplewould have come in and occupied these rock shelters, and they would have eatenthe local resources. and if you notice,this includes a lot of fruit, legumes, agaves,that's what we make tequila from today.

various nuts and beans and squashesand wild game, predominantly rabbits. but by the time april came around, there was very littleedible food in this region so they would have moved on to otherplaces where food was more abundant. so if we take a step back and say, "well, what can we really learn about the palaeolithic dietsaround the world?" there are some generalobservations we can make. one is that they are regionally variable.

people in the arctic haveand will eat something different than people in the tropics. they have different resources. so people who live in placeswith no plants tend to eat more animals, and people who live in placeswhere there are plants tend to eat more plants. they're going to be seasonally variable, because plants seed and fruitat different times, herds migrate and fishspawn on a seasonal cycle.

as these things happen, people have to movefrom resource patch to resource patch, which means that there is periodic highmobility, sometimes over long distances. once again, it depends on the region. food packets were generally small; if you go around collecting wild broccoli, you'll have to collect an awful lot of it to be the equivalentof its domesticated variety. the foods that you would have collected

would have beengenerally tough, woody and fibrous. you would eat meat, but you wouldalso eat the marrow and the organs of the animals you collect,and they'd generally be very lean. finally, the plants you'd eat would still contain a lot of toxinsat various levels, and phytochemicals, some of whichactually have very good health benefits. but it's almost impossiblefor us now to eat this sort of diet. three billion people cannot eatlike foragers on this planet, we are too big.

so, can we take lessonsfrom these palaeolithic diets that we still can applyto our lives today? and the answer is, 'yes.' i think there's three mainlessons we can learn: first, there's no one correct diet,but diversity is the key. so, depending on where you live, you can eat very different things,but you need diversity. we lack the ability to synthesisemany nutrients that we require for life, nutrients and vitamins,

and we are requiredto get them from our foods. eating a diet that's rich in species,has high species diversity is very important. now unfortunately in american diets today, the trend is goingin the opposite direction. if you go and you take a processed foodoff a grocery store's shelf, it doesn't matter if it's cakebatter, mayonnaise or coffee creamer, increasingly there is only three speciesin almost everything we eat. we have corn, soy and wheat.

that's opposite directionwe need to be going. second, we evolved to eat fresh foods,in season, when they are ripe. that's when they have their highestnutritional content. but, of course, we have to also talkabout food storage and preservatives, because in large urban societies, you can't always eateverything fresh; food spoils. some foods preserve naturally well;these include things like seeds and nuts, and that's why traditionally they've beenso important to agricultural populations. but we can preserve them in other ways,through salting, through sugar, vinegar.

we can pickle them, we can smoke them, we can dry them, we can addartificial preservatives. what i find very interesting about thisis that these all work in the same way. they work by inhibiting bacterial growth. but we have to keep in mind that our gastrointestinal systemsare also full of bacteria, good bacteria that domany good things for you: they digest your food,regulate your immune system, promote mucosal function.

if you eat foods full of preservatives, how does that affect your microbiome,your good bacteria within you? and the answer is, 'we really don't know.' and it's somethingwe're only starting to investigate. and third, we evolved to eatwhole foods in their complete package, with their fibreand their roughage and everything. it turns out this is really important, that your foods are not just the sumof the calories and the vitamins. but even the parts you can't digestare very important.

the fibre that you eat regulates the speed at whichthe food travels through your gut. it modulates metabolism,it slows down the release of sugars, it has all sorts of functions, it feedsthe good bacteria that live in your gut. and increasingly we're seeingthat low fibre diets are associated with microbial communities that cause thingslike obesity and diabetes. what's unfortunate also in the globalisedsystem of processed foods is that we're losing these connections,we're losing the whole food,

and we're eating reconstituted,concentrated foods, and we don't get the benefitsof having, for example, the fibre and pectin in the fruit juicebecause it's been filtered out. we're losing all of this balance. and, as an exampleof how this thing gets so out of balance, we can eat so many more calories, so much more food in a very small packagewithout realising it, and that short-circuits our abilities

to know when we're fulland when we've had enough. so i have a question,and my question is, i was wondering, does anyone here know, if you takea soda, let's say a 34 ounce soda, which is increasingly becoming the normalsize, like this one, and you drink it - imagine that you're backin the palaeolithic period, and you want to consumethe equivalent amount of sugar. how much sugar cane,if you stumbled upon a sugar cane field, how much would you have to eat, how many feet of sugar canedo you think you'd have to eat?

i brought some sugar cane. how many feet of sugar cane do you thinkyou'd have to consume to reach that level? any ideas? one... how many sticks do youthink you'd have to eat? they're pretty big. not quite 40 feet. you'd have to eat 8.5 feet of sugar caneto reach that level. that's an awful lot of sugar. there is no physical waythat a palaeolithic person

could have possibly eaten that muchsugar cane, even if they really wanted to, and now you can consumeit in about 20 minutes. so, by decoupling the whole foodfrom the nutrients inside of it, we trick our bodiesand we can override the mechanisms that we've evolved to signalfullness and satiation. these are the three main lessons i thinkwe can learn from real palaeolithic diets: there's no one correct diet,but dietary diversity is key, that we need to eatfresh foods when possible and that we need to eat whole foods.

so, anthropology and evolutionary medicinehave a lot to teach us about ourselves and new technologiesare opening up new windows into the past. but we still have a lot to learn from our palaeolithicand our neolithic ancestors. thank you. (applause)

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